1. Field of the Art
The present invention relates to novel .alpha.-galactosylceramides having effective antitumor activity and immuno-stimulating activity, to a process for producing these .alpha.-galactosylceramides and to the use thereof.
2. Related Art
In respect to .alpha.-galactosylceramide, a study on a mass analysis has been reported in Analytical Chemistry, 59, 1652 (1987), in which the structure of .alpha.-galactosylceramide is described. The compound corresponding to the .alpha.-galactosylceramide has been isolated from a cestode by B. N. Singh and reported in Molecular and Biochemical Parasitology, 26, 99 (1987). However, the stereo chemical configuration of the sugar is not described in the study, and thus the .alpha.-galactosyl structure is not confirmed. In other reports, only two .alpha.-galactosylceramides has been extracted and isolated from the marine sponge Agelas mauritianus by the present inventors (Japanese Patent Application Nos. 303314/1990 and 244385/1991).
On the other hand, it is only those described in Japanese Patent Laid-Open Publication No. 93562/1989 other than the invention according to the present inventors as far as we know that antitumor activity is found for galactosylceramides. Moreover, all of the galactosylceramides in which antitumor activity is shown in Examples of the above cited specification are .beta.-galactosylceramides, and the dosages are as high as 0.5-2 mg per mouse. Furthermore, there is no example in which a galactosylceramide has been used in practice as an antitumor agent or an immunostimulator.
The galactosylceramides derived from marine sponges are described in Japanese Patent Laid-Open Publication No. 57594/1986 and Pure & Applied Chemistry, 58(3), 387-394 (1980). All of these galactosylceramides are, however, .beta.-galactosylceramides, the antitumor activity of which have not been reported.
In general, the physiological activities of chemical substances depend largely on their chemical structures, and it is always desired to obtain novel compounds having antitumor activity and immuno-stimulating activity.